Swift：无法将类型“（）->（）”的值转换为闭包结果类型“Void”

Question

这是所有代码。有一个按钮按下动作函数调用prepareVideo。

@IBAction func nextButtonPressed(_ sender: Any) {

    if MyVariables.isScreenshot == true {
        prepareScreenshot {
            self.moveOn()
        }
    } else {
        prepareVideo()
    }
}  
func prepareVideo(){
        let outputFileName = NSUUID().uuidString
        let outputFilePath = (NSTemporaryDirectory() as NSString).appendingPathComponent((outputFileName as NSString).appendingPathExtension("mov")!)
        self.videoURL = URL(fileURLWithPath: outputFilePath)
        trimVideo(sourceURL: self.footageURL!, destinationURL: self.videoURL!, trimPoints: [(trimmerView.startTime!,trimmerView.endTime!)], completion: prepareVideoThumbnail {
            self.moveOn
        })          //Xcode mentions error here
    }

func trimVideo (sourceURL: URL, destinationURL: URL, trimPoints: TrimPoints, completion: @escaping () -> ()) {

        guard sourceURL.isFileURL else { return }
        guard destinationURL.isFileURL else { return }

        let options = [
            AVURLAssetPreferPreciseDurationAndTimingKey: true
        ]

        let asset = AVURLAsset(url: sourceURL, options: options)
        let preferredPreset = AVAssetExportPresetPassthrough

        if  verifyPresetForAsset(preset: preferredPreset, asset: asset) {

            let composition = AVMutableComposition()
            let videoCompTrack = composition.addMutableTrack(withMediaType: .video, preferredTrackID: CMPersistentTrackID())
            let audioCompTrack = composition.addMutableTrack(withMediaType: .audio, preferredTrackID: CMPersistentTrackID())

            guard let assetVideoTrack: AVAssetTrack = asset.tracks(withMediaType: .video).first else { return }
            guard let assetAudioTrack: AVAssetTrack = asset.tracks(withMediaType: .audio).first else { return }

            var accumulatedTime = kCMTimeZero
            for (startTimeForCurrentSlice, endTimeForCurrentSlice) in trimPoints {
                let durationOfCurrentSlice = CMTimeSubtract(endTimeForCurrentSlice, startTimeForCurrentSlice)
                let timeRangeForCurrentSlice = CMTimeRangeMake(startTimeForCurrentSlice, durationOfCurrentSlice)

                do {
                    try videoCompTrack!.insertTimeRange(timeRangeForCurrentSlice, of: assetVideoTrack, at: accumulatedTime)
                    try audioCompTrack!.insertTimeRange(timeRangeForCurrentSlice, of: assetAudioTrack, at: accumulatedTime)
                    accumulatedTime = CMTimeAdd(accumulatedTime, durationOfCurrentSlice)
                }
                catch let compError {
                    print("TrimVideo: error during composition: \(compError)")
                }
            }

            guard let exportSession = AVAssetExportSession(asset: composition, presetName: preferredPreset) else { return }

            exportSession.outputURL = destinationURL as URL
            exportSession.outputFileType = AVFileType.m4v
            exportSession.shouldOptimizeForNetworkUse = true

            removeFileAtURLIfExists(url: destinationURL as URL)

            exportSession.exportAsynchronously {
                completion()
            }
        }
        else {
            print("TrimVideo - Could not find a suitable export preset for the input video")
        }
    }
func prepareVideoThumbnail(completion: @escaping () -> Void) {
    guard let VideoURL = self.videoURL else { return }
    self.thumbnailImage = setThumbnailFrom(path: VideoURL)
    completion()
    //moveOn()
    //DispatchQueue.main.async {

    //  self.performSegue(withIdentifier: "CreatePost_Segue", sender: nil)
    //}
}

func moveOn(){
        guard self.thumbnailImage != nil else {
            return
        }
        if MyVariables.isScreenshot == true {
            guard self.screenshotOut != nil else {
                return
            }
            self.performSegue(withIdentifier: "CreatePost_Segue", sender: nil)
        } else {
            guard self.thumbnailImage != nil else {
                return
            }
            self.performSegue(withIdentifier: "CreatePost_Segue", sender: nil)
            //now I set those three varibles?
        }
    }

PrepareVideo 不接受回调/完成处理程序，但它调用了 trimVideo，它确实接受了完成处理程序。在这我调用 prepareVideoThumbnail 应该调用它的完成处理程序 { 自我移动 }。 PrepareVideoThumbnail 应该是 trimVideo 怀疑的 () -> () 类型。所以我不确定为什么它抱怨关闭结果类型“无效”。我意识到 self.moveOn() 会导致这种情况，但我没有调用它，请注意我使用的 self.moveOn 没有括号。我该如何解决？

Answer 1

语法：

trimVideo(sourceURL: self.footageURL!, destinationURL: self.videoURL!, trimPoints: [(trimmerView.startTime!,trimmerView.endTime!)], completion: prepareVideoThumbnail {
    self.moveOn
})

应该是：

trimVideo(sourceURL: self.footageURL!, destinationURL: self.videoURL!, trimPoints: [(trimmerView.startTime!,trimmerView.endTime!)]) {
    self.prepareVideoThumbnail() {
        self.moveOn()
    }
}

顺便说一句 - 为不执行任何异步处理的函数（如您的 preparreVideoThumbnail 函数）设置完成参数是没有意义的。

那么你的代码就变成了：

trimVideo(sourceURL: self.footageURL!, destinationURL: self.videoURL!, trimPoints: [(trimmerView.startTime!,trimmerView.endTime!)]) {
    self.prepareVideoThumbnail()
    self.moveOn()
}

并消除prepareVideoThumbnail函数上的完成参数。